The present invention relates to a negative-angle forming die for forming a sheet metal. Herein, the negative-angle forming die is used for a formation made at a location more inward of a lower die half than a straight downward stroke line of an upper die half.
The negatively angled forming of a work provided as a sheet metal into a shape having a portion more inward of the lower die half than the straight downward stroke line of the upper die half is generally performed by using a slide cam.
According to a prior-art intrusion forming process of the sheet metal work, the work is placed on the lower die half and the upper die half is lowered vertically. At this time a drive cam of the upper die half drives a driven cam of the lower die half, forming the work from a side. After the formation is completed and the upper die half is lifted, then the driving cam is retracted by a spring.
In the above arrangement, the driven cam slid onto the work from the side has a forming portion which is formed as a single piece in the same shape as the work as after the formation. The lower die half however, must allow the work to be taken out from the lower die half after the formation, and for this reason, a portion of the lower die half providing the intrusion formation must be made separable for retraction, or a rear portion thereof must be cut off so that the work can be moved forward and taken out. This does not pose a serious problem if the extent of the intrusion is small. However, the problem becomes serious if the extent of the intrusion is large, or if the work is to be formed into a long frame having a groove-like section such as in a formation of an automobile front pillar-outer from a sheet metal. Specifically, since the groove width of the work is so narrow, that if the portion of the lower die half corresponding to the groove is divided or cut off, it becomes impossible for the forming portion of the driven cam to form clearly. In addition, strength of the lower die decreases. Thus, it was impossible to perform a clear-shaped intrusion formation.
Further, a formed product sometimes has a twist or distortion, which must be corrected. However, for example, many automobile parts that provide the outer skin of the automobile, such as a side panel, fender, roof, bonnet, trunk lid, door panel, front pillar-outer and so on are formed to have a three-dimensional surface or line, and therefore it is practically impossible to make correction after the formation. In assembling the automobile sheet-metal parts, if there is a twist or distortion in the parts, it is difficult to fit the parts together. Without solving this problem, it was impossible to provide a high quality automobile sheet metal structure, and it was impossible to maintain a required level of product accuracy in the formed sheet metal products.
In order to solve the above-described problem, an arrangement was proposed, in which the straight downward stroke of the upper die half is converted to a rotary movement of a rotary cam to pivot to form the portion in the lower die half more inward than the straight downward stroke line of the upper die half. In this arrangement, after the forming operation, the rotary cam is pivoted back to a state where the completed work can be taken out of the lower die. This arrangement will be described in more detail.
Specifically, as shown in FIG. 9 to FIG. 12, this negative-angle forming die comprises a lower die half 102 including a supporting portion 101 on which a work W is placed and an upper die half 103 which is lowered straightly down onto the lower die half 102 to press thereby forming the work W. The lower die half 102 is rotatably provided with a rotary cam 106 supported in an upwardly opening axial groove 104. The groove 104 has a portion close to the supporting portion 101 formed with an intrusion forming portion 105 located more inward than a stroke line of the upper die half 103. The lower die half 102 rotatably supports a rotary cam 106. The upper die half 103 is provided with a slide cam 108 opposed to the rotary cam 106 and provided with an intrusion forming portion 107. The lower die half is further provided with an automatic retractor 109 which moves the rotary cam 106 back to the sate that allows the work W to be taken out of the lower die half 102 after the formation. The work W placed on the supporting portion 101 of the lower die half 102 is formed by the intrusion forming portion 105 of the rotary cam 106 and the intrusion forming portion 107 of the slide cam 108. The work W is formed by a rotary movement of the rotary cam 106 and a sliding movement of the slide cam 108. After the formation, the automatic retractor 109 pivots back the rotary cam 106, allowing the work W to be taken out of the lower die half 102.
Now, an operation of this negative-angle forming die will be described.
First, as shown in FIG. 9, the upper die half 103 is positioned at its upper dead center. At this stage, the work W is placed on the supporting portion 101 of the lower die half 102. The rotary cam 106 is held at its retracted position by the automatic retractor 109.
Next, the upper die half 103 begins to lower, and first, as shown in FIG. 10, a lower surface of the slide cam 108 makes contact with a pivoting plate 111 without causing the slide cam 108 to interfere with the intrusion forming portion 105 of the rotary cam 106, pivoting the rotary cam 106 clockwise as in FIG. 10, thereby placing the rotary cam 106 at a forming position. Then, a pad 110 presses the work W.
When the upper die half 103 continues to lower, the slide cam 108 which is under an urge outward of the die half begins a sliding movement as the sliding cam in a laterally leftward direction, against the urge from a coil spring 112. This is a state shown in FIG. 11, where the intrusion forming portion 105 of the pivoted rotary cam 106 and the intrusion forming portion 107 of the slide cam 108 perform formation of the work W.
After the intrusion formation, the upper die half 103 begins to rise. The slide cam 108, which is urged outwardly of the die half by the coil spring 112, moves in a laterally rightward direction as in FIG. 12, and keeps rising without interfering with the work W as after the intrusion formation. On the other hand, the rotary cam 106 is released from the holding by the slide cam 108, and therefore is pivoted in a leftward direction as in FIG. 12 by the automatic retractor 109. Thus, when the work W is taken out of the lower die half after the intrusion formation, the work W can be removed without interference with the intrusion forming portion 105 of the rotary cam 106.
According to the negative-angle forming process described above, the lower surface of the slide cam 108 urged by the coil spring 112 contacts the pivoting plate 111 urged by the coil spring 113 of the automatic retractor 109, rotating the rotary cam 106 in the clockwise direction to the shaping position, and thereafter, the pad 110 presses the work W. With this arrangement, urging force from the pad 110 to the work W is so strong that the work W under the formation can be slightly pivoted counterclockwise as in the figure. In another case, the urge of the coil spring 112 of the slide cam 108 is not well balanced with the urge of the coil spring 113 of the automatic retractor 109, resulting in a slight pivoting movement of the rotary cam 106 out of the predetermined position for the formation. These situations sometimes make impossible to form into an accurate curve. For example, it is sometimes impossible to provide a product of an accuracy level in the order of {fraction (1/100)} mm, and it was sometimes impossible to achieve a high quality negative-angle formation.
Further, as will be understood from FIG. 9 through FIG. 12, the rotary cam 106 is supported by the lower die half 102 through direct contact of the cam""s outer circumference except for the groove portion 104. With this structure, accurate and difficult machining must be made to the rotary cam 106 and the supporting portion (a bore having a generally circle section) of the lower die half 102 which supports the rotary cam 106.
Further, since most of the outer wall of the rotary cam 106 is used for support by the lower die half 102, the negative angle forming die tends to be large and expensive.
Now, in consideration of the background described above, the present invention aims to solve these problems: that slight pivoting movement makes a rotary cam out of a predetermined forming position, making an unwanted step in a curved surface of the work or making unable to form into an accurate curve; that it is difficult to provide a product of accuracy in the order of {fraction (1/100)} mm is difficult; and that it is impossible to provide a formed sheet metal product of a high quality. The present invention aims to maintain the rotary cam at a predetermined forming position thereby providing a formed sheet metal product of a high quality. In order to achieve this object, the present invention provides a negative-angle forming die comprising a lower die half having a supporting portion for placing a sheet metal work, and an upper die half to be lowered straightly downward onto the lower die half for forming the work, an intrusion forming portion formed in the lower die half at an edge portion near the supporting portion inward of a downward stroke line of the upper die half, a rotary cam rotatably provided in the lower die half, a slide cam including an intrusion forming portion and slidably opposed to the rotary cam, and an automatic retractor provided in the lower die half for pivoting the rotary cam back to a position thereby allowing the work to be taken out of the lower die half after a forming operation, the work placed on the supporting portion of the lower die half being formed by the intrusion forming portion of the rotary cam and the intrusion forming portion of the slide cam, the slide cam forming the work by sliding, the automatic retractor pivoting back the rotary cam after the forming operation for allowing the work to be taken out of the lower die half, wherein the rotary cam has two ends each including a supporting shaft projecting therefrom, the supporting shafts being supported by the lower die half for rotatably supporting the rotary cam, positioning means for fixing an axial position of the rotary cam being provided in the lower die half and the rotary cam.
Further, in consideration of the background described above, the present invention aims to solve these problems: that slight pivoting movement makes a rotary cam out of a predetermined forming position, making an unwanted step in a curved surface of the work or making unable to form into an accurate curve; and it is difficult to provide a product of accuracy in the order of {fraction (1/100)} mm is difficult; and that it is impossible to provide a formed sheet metal product of a high quality. The present invention aims to minimize the unwanted movement of the rotary cam at the time of the intrusion formation and maintain the rotary cam at a predetermined forming position, thereby providing a formed sheet metal product of a high quality. In order to achieve this object, the present invention provides a negative-angle forming die comprising a lower die half having a supporting portion for placing a sheet metal work, and an upper die half to be lowered straightly downward onto the lower die half for forming the work, an intrusion forming portion formed in the lower die half at an edge portion near the supporting portion inward of a downward stroke line of the upper die half, a rotary cam rotatably provided in the lower die half, a slide cam including an intrusion forming portion and slidably opposed to the rotary cam, and an automatic retractor provided in the lower die half for pivoting the rotary cam back to a position thereby allowing the work to be taken out of the lower die half after a forming operation, the work placed on the supporting portion of the lower die half being formed by the intrusion forming portion of the rotary cam and the intrusion forming portion of the slide cam, the slide cam forming the work by sliding, the automatic retractor pivoting back the rotary cam after the forming operation for allowing the work to be taken out of the lower die half, wherein the rotary cam has two ends each including a supporting shaft projecting therefrom, the supporting shafts being supported by the lower die half for rotatably supporting the rotary cam, a backup portion being formed in the lower die half for supporting a surface of the rotary cam on a side away from a side receiving the slide cam.
Further, the present invention does not rely on the multi-diameter rotary cam in a case in which there is a large variation in the distance of the intrusion forming portion from the axis. Specifically, the present invention provides a negative-angle forming die, wherein the intrusion forming portion varies a pressing side-portion of the rotary cam contacted by the backup portion in accordance with a distance from an axis of pivoting.